Probe systems of this kind are used, for example, for sensing the positions of workpieces which are clamped into material-working machines, such as milling machines. These probe systems often have a stationary transceiver unit which is secured to a fixed element of the material-working machine, and a part that is movable or mobile relatively thereto, which is often described as a probe head that is mounted on a movable element of the material-working machine, for example, on a milling spindle. In this context, the probe head includes a feeler or probe element that is deflectable out of a rest position and that generates a switching signal in response to a deflection out of its rest position. Rest position of the probe element is understood to be a position where the probe element does not have any contact with a workpiece. In response to contact of the probe element with the workpiece, the probe element is deflected out of its rest position.
In so-called wireless probe systems, the corresponding switching signal is transmitted by the probe head as an electromagnetic signal, e.g., as an infrared signal, to the stationary transceiver unit. In the transceiver unit, the output signals of the probe system are analyzed in order to determine the occurrence of switching signals (thus a deflection of the probe element).
For its energy supply, such a probe head often has a direct-current source in the form of one or more batteries. There is a constant desire to increase the operating availability of such probe systems, which is why there is an effort to maximize the service life of the direct-current sources. For this reason, outside of the measuring-operation times, the probe head is usually in a standby state.
European Published Patent Application No. 1 179 173, for example, describes a battery-operated probe head, for which the intention is to prolong the service life of the batteries by various measures, which ultimately improves the uptime of the respective probe system because of less frequent standstill times due to exhausted batteries.
So that the availability may be increased over and above that, the service life may be increased by using high-quality, but expensive batteries, e.g., lithium batteries. However, such batteries have only a relatively limited shelf life, because due to passivation effects, these batteries no longer supply the nominal voltage after a certain time. If, after an operating time of targeted length, a probe head is equipped with such batteries which have been stored too long, it cannot be operated. Incidentally, in the following, the term battery is intended to include both a non-rechargeable battery, as well as a rechargeable battery.